1. Field of the Invention
The present invention relates to lane boundary line information acquiring devices capable of correctly recognizing lane boundary lines on a roadway on which an own vehicle drives and supporting correct driving assist such as a lane keeping control and a lane departure warning even if a visibility of lane boundary lines is not reduced.
2. Description of the Related Art
Recently, there has been developed and known a technology for detecting lane boundary lines on a roadway on which an own vehicle drives on the basis of images around the own vehicle acquired by an in-vehicle camera. For example, there are white lines, Botts' dots, cat's eyes, etc. as the lane boundary lines. Such cat's eyes are retro-reflective safety devices used in road making. First, pixels having a large brightness-change in the acquired images are extracted as edge points. A trend curve passing the extracted edge points is detected as a lane boundary line on the roadway on which the own vehicle drives. The detected lane boundary line is used for performing driving assist such as lane keeping assist control (LKA control) and lane departure warning.
However, there is a possible case of it being difficult to correctly detect a lane boundary line from the images captured by the in-vehicle camera due to a road-surface condition, etc. If a control device of the own vehicle executes the lane keeping control on the basis of incorrect lane boundary line information, there is a possible case of performing an incorrect assist control of the own vehicle. In order to avoid such an incorrect assist control, a conventional technique, disclosed in a patent document 1, Japanese patent laid open publication No. 2014-26608, judges a visibility of lane boundary lines on the basis of a total number of edge points extracted from images captured during the lane boundary line detection. When the judgment result indicates the visibility is low, the control device of the own vehicle stops providing a lane departure warning to the driver of the own vehicle.
When the technique of the patent document 1 previously described is applied to the lane keeping control, it is possible to stop the execution of the lane keeping control only when the detection result indicates occurrence of a low visibility of lane boundary lines. For this reason, the control device of the own vehicle continues to execute the lane keeping control under a low visibility of lane boundary lines before the low visibility of lane boundary lines is detected.